Medium-pressure hydrocracking process

ABSTRACT

The present invention discloses a medium-pressure hydrocracking process able to simultaneously produce products such as qualified gasoline, kerosene, diesel, etc.. Based on the prior medium-pressure hydrocracking process, the present invention uses a fresh hydrogen resource and a hydrosaturation catalyst with reduced metals of group VIB and/or group VIII as the active components to selectively and deeply hydrosaturate the jet fuel and/or diesel cuts derived in the medium-pressure hydrocracking, thereby allowing the quality of these cut fractions to meet the requirement of the specifications. In the present invention, a quite favorable reaction environment is created for the deep hydrosaturation of the jet fuel and/or diesel cuts with an extremely low investment by reasonable combination of the medium-pressure hydrocracking process flow, full reliance on the medium-pressure hydrocracking,, and addition of an ultra-low-pressure hydrosaturation reactor. This makes it possible to not only simultaneously produce products such as qualified gasoline, kerosene, diesel, etc., but also further lower the operation pressure of the hydrocracking since the requirement for the quality of such products as the hydrocracked jet fuel, diesel, etc. is broadened.

FIELD OF THE INVENTION

[0001] The present invention relates to a process for producing highquality motor fuels, especially a medium-pressure hydrocracking process,from low quality heavy oils.

BACKGROUND OF THE INVENTION

[0002] Along with the continuous development of the world economy, thedemand of the market for the petrochemical products is continuouslyincreasing. However, the resource of low sulfur crude oil in manycountries is insufficient. Therefore there is a need to process a greatamount of imported high sulfur crude oil. This sets a task in front ofmost refineries with FCC as the main equipment as to how to reform so asto meet the need of processing high-sulfur crude oil. The experience inprocessing high-sulfur crude oil in various countries shows that thehydrocracking process is a major means to convert high sulfur heavyoils. However, the high investment resulted from the high-pressurehydrocracking, equipment and the great demand for the hydrogen resourcegreatly limits the rapid development of the hydrocracking process.Therefore refiners are eager to find out a new process for solving thisproblem.

[0003] Hydrocracking is generally operated at a pressure level of 15.0MPa and has many advantages such as high operation flexibility, highproduct quality, etc., but also has such disadvantages as a highinvestment in the construction and a high consumption of hydrogen. Thedisadvantages are more severe when there is lack of funds and of cheaphydrogen sources such as natural gas. However, because of the variousadvantages exhibited by the hydrocracking process in processing highsulfur crude oil, the hydrocracking process still possesses superiorstatus and function to those non-hydrotreating processes, and thereforebecomes one of the first choices made by refinery engineers inprocessing high sulfur crude oil. In order to overcome the shortcomingsof the hydrocracking, technology, people started to explore long ago tofind out whether it is possible to lower the operation pressure of thehydrocracking process and have made great advances. Medium-pressurehydrocracking or medium-pressure hydroupgrading technologies have beensuccessfully developed (e.g. U.S. Pat. No. 4,971,680), with an operationpressure being about 8.0 MPa. The product quality is greatly affected inthe medium-pressure hydrocracking due to the intrinsic shortcoming oflow saturation extent of aromatics limited by the thermodynamicequilibrium. Particularly to the jet fuel, since a great amount ofaromatics are transferred during the reaction to such a cut fraction andcan not be saturated effectively, its quality specifications such as thesmoking point, etc., can not meet the requirements. This greatly limitsthe scope of the lowering in the operation pressure of themedium-pressure hydrocracking process. Nowadays, the operation pressureindustrially adopted in the medium-pressure hydrocracking processes isabout 10.0 MPa, and most of the processes can not be directly used toproduce jet fuel. Also, the quality of diesel is hard to attain thespecifications of the World Standard III for diesel. The improvingeffect of lowering the operation pressure on the investment andoperating cost is not distinct, but the product quality is lowedsharply. Therefore, there has not been a breakthrough in the developmentand application of the medium-pressure hydrocracking process for a longtime.

THE DISCLOSURE OF THE INVENTION

[0004] The objective of the present invention is to develop amedium-pressure hydrocracking process, which shall retain the abovementioned advantages of hydrocracking process, while overcoming itsshortcomings of high investment and high consumption of hydrogen. To bemore exact, the purpose of the present invention is to solve the qualityproblem of the product brought about by the insufficient saturation ofaromatics, especially the quality problem of the jet fuel product.

[0005] The major problem of the hydrocracking under a lowered pressureis the increased aromatics content in the product resulted from theinsufficient hydrogenation capacity. For naphtha, the increase in thearomatics content does not bring about adverse effects because naphthacan be used as a reforming feed, and oppositely, the increase in thearomatics content can reduce the severity of the operation of thecatalytic reforming and the unnecessary consumption of hydrogen. For thediesel cut, the quality specifications such as cetane number, etc., aregreatly surplus because the content of aromatics in the correspondingproduct of high-pressure hydrocracking is low. When the operationpressure is lowered, the hydrogen consumption and the hydrosaturationdepth are lowered, but the requirement for the quality specificationscan still be met in many cases, and the process becomes more reasonablefrom the economic viewpoint. However, the content of aromatics is animportant factor affecting the quality of the product jet fuel. Thecontent of aromatics and the smoking point are two key specifications ofjet fuel, and the higher the content of aromatics, the lower the smokingpoint is. In most cases, the specifications of the jet fuel produced inmedium-pressure hydrocracking, such as the content of aromatics, thesmoking point, etc., are not qualified. The factors affecting theactivity of the hydrosaturation in the hydrocracking process are of bothkinetic and thermodynamic aspects. Kinetically, the activity of thehydrogenation component in the catalyst is very high, but thehydrogenation activity of the catalyst can not fully bring into playbecause of the poisoning effects of H₂S, NH₃ and the impurities such asorganic sulfur nitrogen, etc. in the feed. Therefore, the reactiontemperature has to be raised so that the reaction can be accelerated,and the cracking reaction generally demands relatively hightemperatures. However, high temperatures are thermodynamicallyunfavorable to the hydrosaturation reaction. Under the conditions of thehigh-pressure hydrocracking, the partial pressure of hydrogen cancompensate the adverse effects of the temperature on the thermodynamicequilibrium, while under the conditions of the medium-pressurehydrocracking, the effects of the reaction temperature on thethermodynamic equilibrium attain an extent that can not be neglected.

[0006] U.S. Pat. No. 4,172,815 describes a process for producing jetfuel and diesel wherein the tail oil is completely recycled. Heavy cutfractions pass through a hydrocracking reactor, and the jet fuelfraction in the effluent is then fractionated out and partly recycled sothat the smoking point of the jet fuel is raised. But this process hasobvious disadvantages so that it is only applicable to those processflows wherein the smoking point of the jet fuel is relatively high andtherefore an elevation thereof of only 2-3 mm would meet therequirement. However, the smoking point of the jet fuel produced in amedium-pressure hydrocracking process is generally lower than 20 mm, andtherefore the use of this process is restricted under medium pressures.Especially, the recycle of a part of the jet fuel will certainly lowerits yield and affect the capacity of the hydrocracking equipment orincrease the investment in the hydrocracking equipment.

[0007] U.S. Pat. No. 5,026,472 discloses a process, wherein the jet fuelcut and the hydrogen-containing vapor in the effluent of thehydrocracking are separated by adjusting the pressure and temperature ofa two stage vapor-liquid separator, and the separated jet fuel and apart of the hydrogen-containing vapor enter into a hydrogenation reactorfor hydrogenation of the jet fuel, while the remaininghydrogen-containing vapor enters the hydrocracking reactor. Because ofthe post-processing of the jet fuel component, a qualified jet fuelproduct can be produced under a medium to high pressure. But thedisadvantages are that the process flow is complex, the amount ofhigh-pressure equipment is great, and the increase in the investment ismore, so that the superiority of the medium-pressure can not bematerialized. And since the oil vapor entering the refining reactorstill contains a great amount of impurities such as H₂S, NH₃, H₂O, etc.,the hydrosaturation performance of the catalyst in the hydrogenationreactor of the jet fuel degrades, and the sorts of the applicablehydrogenation catalysts are limited too. For instance, most of the noblemetal catalysts or non-noble metal saturation catalysts in reducedstates are not applicable.

[0008] The object of the present invention is to overcome theshortcomings of medium-pressure hydrocracking process that it isdifficult to directly produce qualified jet fuel and high qualitydiesel, thereby improving its practicability.

[0009] For convenience of description, the medium-pressure hydrocrackingunit of the present invention is divided into a medium-pressurehydrocracking system, a hydrosaturation system, and a separation system.The medium-pressure hydrocracking system consists of a hydrocrackingequipment (such as a reactor) and heating and heat-exchanging equipmentwhere necessary. The flow of the medium-pressure hydrocracking systemcan be particularly designed according to the practical needs. Forexample, it may be a single stage hydrocracking flow, i.e., the feed oildirectly enters into a reactor in which a hydrocracking catalyst ischarged to carry out the reaction, without a pre-reaction section forhydrotreating being equipped; or it may also be a two-stagehydrocracking flow, i.e., including a hydrotreating section and ahydrocracking section, so that the feed oil first enters into thehydrotreating section, in which such impurities as H₂S and NH₃ areremoved from the reactants, and then enters into the hydrocrackingsection for cracking. Of course, the process flow may also comprise ahydrotreating section and a hydrocracking section, in which thereactants from the hydrotreating section directly enter into thehydrocracking section without first removing the impurities such as H₂S,NH₃, etc. therefrom. The hydrosaturation system consists of ahydrosaturation reactor and a liquid-vapour separator. The separationsystem may be selected, according to the particular situation, from agroup consisting of a low separator, a stripping tower, a fractionationtower, etc.

[0010] According to the present invention, the feed oil enters into amedium-pressure hydrocracking system under a medium pressure andhydrocracking conditions to carry out the reaction, and the reactionproduct is separated into vapor and liquid phases in, for example, ahigh pressure vapor-liquid separator. The vapor phase product isrecycled to said medium-pressure hydrocracking system as recyclinghydrogen; and the liquid phase enters into a separation system, whereinit is separated into distillates including jet fuel and/or diesel(hereinafter referred to as hydrocracked jet fuel and/or diesel) cuts,for example, liquefied petroleum gas, naphtha, jet fuel, diesel, andtail oil. Then, a part or all of the hydrocracked jet fuel and/or dieselcuts enter a hydrosaturation system, comes into contact with ahydrosaturation catalyst and reacts with fresh hydrogen underhydrosaturation conditions. The hydrosaturation reaction product is thenseparated through a vapor-liquid separator into a hydrogen-containingvapor which enters into the medium-pressure hydrocracking system asmake-up hydrogen, and jet fuel and/or diesel (hereinafter refered to asthe hydrosaturated jet fuel and/or diesel) which enter into a separationsystem for processing.

[0011] As mentioned above, the jet fuel produced from a medium-pressurehydrocracking treatment is not easy to meet the required specifications,while sometimes the produced diesel can. So, if the quality of thediesel happens to meet the specifications, only the jet fuel separatedin the separation system shall be sent to a hydrosaturation system forfurther processing. However, if neither the diesel nor the jet fuelmeets the specifications, both of them can be sent together to ahydrosaturation system for further processing. Of course, it iscertainly permissible to merely send diesel to a hydrosaturation systemfor processing according to certain particular situations.

[0012] Said hydrosaturated jet fuel and/or diesel derived in the aboveprocess of the present invention preferably enter into an individualseparation system for processing. In case that jet fuel and diesel arehydrosaturated together, the mixed distillate of jet fuel and diesel canbe separated through said individual separation system and mayseparately leave the equipment. If merely one of them is required toenter into a hydrosaturation system for processing, or jet fuel anddiesel separately enter into the hydrosaturation system without mixing,the hydrosaturated jet fuel or diesel may leave the equipment asproducts merely by simple stripping without any further processing.

[0013] In case that the hydrosaturated jet fuel and/or diesel enter intoan individual separation system for processing, the hydrocracked jetfuel and/or diesel cuts may either completely or partly enter into thehydrosaturation system for processing and the remainder (where partlyentering) is mixed together with the corresponding hydrosaturated jetfuel or diesel product and leave the equipment.

[0014] According to the medium-pressure hydrocracking process of thepresent invention, the jet fuel and/or diesel cuts derived through theprocessing in the hydrosaturation system may also be returned to thesame separation system, in which the hydrocracked liquid product isseparated, for fractionation together with the hydrocracked liquidproduct. In this case, only a part of the jet fuel and/or diesel derivedfrom the separation system is allowed to enter the hydrosaturationsystem for processing and the remainder leaves the equipment asproducts. The weight ratio of the jet fuel and/or diesel cuts enteringinto the hydrosaturation system to those leaving the equipment asproducts (abbreviated as reflux ratio below) generally ranges from 1:6to 6:1 depending on the desired product quality.

[0015] According to the present invention, the medium-pressurehydrocracking conditions used in the hydrocracking system generally are:reaction temperature 360-400° C., pressure 4.0-10.0 MPa, preferably4.0-8.0 MPa, hydrogen/oil volume ratio 800:1-1500:1, and space velocity0.5-1.5 h⁻¹. The catalysts used in said hydrocracking process are any ofthose which are suitable for the medium-pressure hydrocracking processincluding the existing medium-pressure hydrocracking catalysts, such asthose as disclosed in U.S. Pat. No. 6,043,178, U.S. Pat. No. 5,026,472,U.S. Pat. No. 4,172,815, etc.

[0016] Generally speaking, the hydrosaturation catalysts described inthe present invention are any of those which can hydrosaturate the jetfuel and/or diesel cuts in the hydrosaturation system, and arepreferably selected from the reduced noble metals or non-noble metals ofGroups VIB and/or VIII in the Periodic Table as the hydrogenationcomponent, more preferably one or more metals selected from the groupconsisting of Pt, Pd, and Ni as the hydrogenation components of thereduced catalysts. The supports of such catalysts may be any of thesuitable materials, such as refractory inorganic materials like alumina,silica, et al., as well as Y-, β- type molecular sieves. For instance,the noble metal catalysts as disclosed in CN 1,053,636, and thenon-noble catalysts as disclosed in CN 89,106,476 are suitable as thehydrosaturation catalysts of the present invention.

[0017] The process conditions used in the hydrosaturation are: reactiontemperature 100-280° C., preferably 100-250° C., reaction pressure0.5-3.0 MPa, preferably 1.0-2.0 MPa; hydrogen/oil volume ratio200:1-1000:1; liquid hourly volume space velocity 1.0-6.0 h⁻¹.

[0018] The feed oil suitable for the process of the present inventionmay be the heavy oil cuts suitable for a medium-pressure hydrocrackingprocess, such as the feed oil as described in U.S. Pat. No. 5,026,472,the vacuum distillates from the vacuum distillation devices ofrefineries, etc.

[0019] The fresh hydrogen described in the present invention may comefrom a hydrogen production system or the pipe net of the refinery. Thefresh hydrogen substantively contains no impurities such as H₃S, NH₃,etc. and need not be further pressurized when used in the presentinvention.

[0020] The medium-pressure hydrocracking process of the presentinvention has the following characteristics compared with the priorarts:

[0021] 1. On the basis of the prior hydrocracking process flow,recycling flow of a part or the whole of the jet fuel and/or diesel cutsis added, so that the low quality kerosene and/or diesel obtained in themedium-pressure hydrocracking are further improved and become highquality jet fuel and/or diesel products.

[0022] 2. The kinetic and thermodynamic characteristics of thehydrosaturation reaction are fully considered from the angle of theprocess flow, so that the hydrosaturation reactions of the jet fueland/or diesel occur under the optimum conditions, whereby the efficiencyof the catalytic reaction is greatly raised.

[0023] 3. The catalysts having high hydrosaturation activity andcontaining reduced metals of group VIB and/or group VIII may be used inthe hydrosaturation reaction of the jet fuel and/or diesel cuts so thatthe reaction conditions are very mild, For example, the reaction may beperformed under a pressure of the hydrogen source of the system, at atemperature of the corresponding cut fractions at the time of beingwithdrawn from the side-line of the separation system following thehydrocracking system, and so on.

[0024] 4. Fresh hydrogen containing no catalyst poisons for thehydrosaturation reaction such as H₂S, NH₃, etc. is first used tohydrosaturate the jet fuel and/or diesel from hydrocracking, so thathigh activity of the hydrosaturation reaction is ensured.

[0025] 5. The hydrosaturation of the jet fuel and/or diesel cuts derivedin the hydrocracking has the particular advantage that thehydrosaturation catalyst can not be deactivated by poisons since theimpurities like sulfur, nitrogen, etc. in the jet fuel and/or dieselcuts are substantively removed, whereby the conduction of the saturationof the aromatics with high efficiency is ensured.

[0026] 6. The use of the reduced hydrosaturation catalysts preferablyrecommended by the solution of the present invention makes it possibleto perform the hydrosaturation reaction of the jet fuel and/or diesel atlower pressures, whereby the investment in the equipment and theoperating cost are greatly lowered.

[0027] 7. The use of partial or complete recycle flow of the jet fueland/or diesel has the advantages of the simplification of the processflow and the full use of the capacity of the hydrocracking equipment, sothat the increase in the investment in the medium-pressure hydrocrackingprocess of the present invention is very little compared with that inthe corresponding conventional medium-pressure hydrocracking process. Inmost cases, the investment in the medium-pressure hydrocracking processof the present invention is even lower. In particular, the use of freshhydrogen to first hydrosaturate the jet fuel and/or diesel cuts beforethe fresh hydrogen enters into the hydrocracking system makes itpossible to fully and repeatedly use the fresh hydrogen system in caseof very limited investment. Since the saturation of the aromatics in thejet fuel and/or diesel cuts can be performed in the hydrosaturationsystem, the operation pressure of the hydrocracking system can befurther lowered, whereby the investment in the equipment is greatlyreduced.

[0028] 8. The combination of the hydrosaturation of the jet fuel and/ordiesel cuts with the medium-pressure hydrocracking permits the precioushydrogen resource to be fully, effectively and reasonably utilized.Comparatively, the new process both retains the advantages of the priormedium-pressure hydrocracking, and overcomes the shortcoming of theprior medium-pressure hydrocracking that the hydrosaturation depth ofthe jet fuel and/or diesel cuts can not be ensured. In other words, thenew process makes it possible to concentrate the limited hydrogenresource on the deep hydrosaturation of the jet fuel and/or diesel cutsso that the unnecessary deep hydrogenation of naphtha as inhigh-pressure hydrocracking is avoided.

[0029]FIG. 1 shows an embodiment of the present invention, in which thehydrosaturated product and the hydrocracked, separated liquid productenter the same separation system.

[0030]FIG. 2 shows an embodiment of the present invention, in which thehydrosaturated product and the hydrocracked, separated liquid productenter different separation systems respectively.

[0031] The technical solution of the present invention is describedbelow in combination with the drawings.

[0032] As shown in FIG. 1, the feed oil from line 1 is, afterpressurized by oil pump 2, mixed with the hydrogen-containing vapor fromphase separator 12 and pressurized by make-up hydrogen compressor 18 andthe recycling hydrogen from recycle compressor 5, and fed intohydrocracking system 3 to react. After cooled by heat exchange, thereaction product is separated into a vapor phase and a liquid phasethrough a high pressure separator 4. The vapor phase is pressurized andrecycled by recycle compressor 5, and the liquid phase is separated intodifferent products according to the boiling points of the cut fractionsin following distillation system 6. The liquefied petroleum gas leavesthe equipment through line 13; the light and heavy naphthas leave theequipment through lines 14 and 15 respectively. The tail oil can eitherbe partly or completely recycled back to hydrocracking system 3 throughline 10 for processing, or partly or completely leave the equipmentdirectly through line 11. A part of the separated jet fuel cut withdrawnthrough line 16 and/or the diesel cut withdrawn through line 17 canpartly mix with the fresh hydrogen from line 9 by recycle pump 7 andenter into hydrosaturation reactor 8, and the product of thehydrosaturation goes to phase separator 12 for vapor-liquid separation.The vapor phase goes to the cracking system 3 after pressurization bysupplement hydrogen compressor 18, and the liquid phase returns toseparation system 6.

[0033] As shown in FIG. 2, the feed oil from line 1 is, afterpressurized by oil pump 2, mixed with the hydrogen-containing vapor fromphase separator 12 and pressurized by make-up hydrogen compressor 18 andthe recycling hydrogen from recycle compressor 5, and fed intohydrocracking system 3 to conduct the reaction. After cooled by heatexchange, the reaction product is separated into a vapor phase and aliquid phase through high separator 4. The vapor phase is pressurizedand recycled by recycle compressor 5, and the liquid phase is separatedinto different products according to the boiling points of the cutfractions in following distillation system 6. The liquefied petroleumgas leaves the equipment through line 13; the light and heavy naphthasleave the equipment through lines 14 and 15 respectively. The tail oilcan either be partly or completely recycled back to the hydrocrackingsystem 3 through line 10 for processing, or partly or completely leavethe equipment directly through line 11. A part of the separated jet fuelcut withdrawn through line 16 and/or the diesel cut withdrawn throughline 17 can partly or completely mix with the fresh hydrogen from line 9by recycle pump 7 and enter into hydrosaturation reactor 8, and theproduct of the hydrosaturation goes to phase separator 12 forvapor-liquid separation. The vapor phase goes to the cracking system 3after pressurization by make-up hydrogen compressor 18, and the liquidphase goes to separation system 21 directly. The jet fuel cut withdrawnthrough line 19 and/or the diesel cut withdrawn through line 20separated in the separation system leave the equipment as the finalproducts. If the aforesaid jet fuel cut withdrawn through line 16 and/orthe diesel cut withdrawn through line 17 are partly recycled tohydrosaturation system 8 for processing, the remainder mixes with thecorresponding jet fuel withdrawn through line 19 or the diesel withdrawnthrough line 20 and leaves the equipment together as the final product.

[0034] The effects of the technical solutions of the present inventionare further explained by the following Examples.

[0035] Table 1 shows the major properties of a typical feed oil formedium-pressure hydrocracking, and this feed is used in all thefollowing Examples and Comparative Examples.

COMPARATIVE EXAMPLES 1-2

[0036] A medium-pressure hydrocracking process comprising ahydrotreating step and a hydrocracking step in series is used. Theprocess conditions used and product distribution are shown in Table 2.The properties of the jet fuel produced are shown in Table 3. It can beseen from Table 3 that the jet fuel produced in the medium-pressurehydrocracking process contains more aromatics, and the smoking point is16-18 mm, so the requirement of the specifications for the jet fuelcannot be met. Therefore, the applicability of this medium-pressurehydrocracking process is greatly limited. The properties of the dieselproduced are shown in Table 4. It can be seen from Table 4 that thevolume contents of the aromatics of the diesel produced in themedium-pressure hydrocracking process are lower than 25%, but higherthan 15%. The cetane number is even lower than 45 at 5.0 MPa, which doesnot attain the required specifications for diesel.

EXAMPLES 1-3

[0037] On the basis of the hydrocracking process of Comparative Examples1-2, only a hydrosaturation system is added. Jet fuel and other productsare produced under different process conditions. The process flow isshown in FIG. 1. Table 5 shows the process conditions and results. Itcan be seen from Table 5 that in the jet fuel produced using the processof the present invention, the content of aromatics is greatly lowered,and smoking point of the jet fuel is raised, so it is a high quality jetfuel.

EXAMPLES 4-5

[0038] On the basis of the hydrocracking process of Comparative Example2, only an individual hydrosaturation system of diesel (Example 4), or amixing hydrosaturation system of jet fuel and diesel (Example 5) isadded. Jet fuel and/or diesel products are produced under differentprocess conditions. Refer to FIG. 2 for the process flow. In Example 4,the diesel cut separated from the hydrocracking product by theseparation system completely enters into the hydrosaturation system forprocessing. In Example 5, the jet fuel and diesel cuts separated fromthe hydrocracking product by the separation system completely enter intothe hydrosaturation system for processing. The process conditions andresults of Examples 4 and 5 are shown in Tables 5-6. It can be seen fromTable 6 that in the diesel produced using the process of the presentinvention, the content of aromatics is greatly lowered, and the cetanenumber is greatly raised. And therefore the process of the presentinvention is able to produce the diesel product which accords with theworld fuel standard III. In case of the mixing hydrogenation of jet fueland diesel (Example 5), the aromatics and smoking point etc. of the jetfuel (Table 5) also entirely meet the specifications. TABLE 1 Propertiesof the feed oil Density (20° C.), g/cm³ 0.9047 Distillation range, ° C.IBP/10% 328/376 30%/50% 403/423 70%/90% 440/466 95%/EBP 483/508 Sulfur,wt % 0.55 Nitrogen, μg/g 1599

[0039] TABLE 2 Reaction conditions and product distribution ComparativeComparative No. of Comparative Example Example 1 Example 2 Catalyst 3936/3905*  3936/3905* Pressure, MPa 7.5 5.0 Temperature, ° C. 377/380380/380 LHVSV**, h⁻¹  0.9/1.60 0.7/1.6 Hydrogen/oil volume ratio 1000:11000:1 Product distribution, ° C.  <82 6.5 6.3  82-132 12.1 11.7 132-28236.3 36.5 282-350 9.3 14.3 >350 32.8 28.2

[0040] TABLE 3 Properties of the jet fuel produced in ComparativeExamples 1-2 Comparative Comparative No. of Comparative Example Example1 Example 2 Density (20° C.), g/cm³ 0.8173 0.8195 Distillation range, °C. ASTM D 86 ASTM D 86 IBP/10% 148/164 148/165 30%/50% 179/198 177/19470%/90% 219/244 215/240 98%/FBP 261/263 255/260 Freezing point, ° C.<−60 <−60 Flashing point, ° C. 39 40 Smoking point, mm 18 16 Aromatics,v % 20.9 24.4 Sulfur content, μg/g 3 1

[0041] TABLE 4 Properties of the diesel produced in Comparative Examples1-2 Comparative Comparative No. of Comparative Example Example 1 Example2 Density (20° C.), g/cm³ 0.8459 0.8601 Distillation range (° C., ASTM270-345 266-343 D 86) Freezing point, ° C. −5 −9 Flashing point, ° C.155 140 Cetane number 49 41 Aromatics, v % 18.9 24.3 Sulfur content,μg/g 3.5 5

[0042] TABLE 5 Results of hydrosaturation of the jet fuel produced bythe present invention Example No. Example 1 Example 2 Example 3 Example5 Type and No. Reduced Reduced Reduced Reduced Of Catalyst non-noblenon-noble noble metal non-noble metal metal catalyst C metal catalyst Acatalyst B catalyst A Physical properties of the catalysts before useContent of Elementary Elementary Pd/Pt atom Elementary metals* nickel,nickel, ratio = nickel, 34 wt % 29 wt % 0.2 34 wt % Nickel Nickel Pd +Pt = Nickel oxide, oxide, 1.0 wt % oxide, 20 wt % 17 wt % 20 wt %Alumina, wt % Balanced Balanced Balanced Balanced Specific 156 142 302156 surface area, m²/g Pore volume, 0.25 0.28 0.31 0.25 ml/g Processconditions Reflux ratio of  1:1  3:1  1:3 jet fuel Hydrogen 1.2 1.3 3.01.5 partial pressure, MPa Temperature, 120 130 250 200 ° C. LHVSV**, h⁻¹2.0 3.0 4.0 2.0 Hydrogen/oil 300:1 400:1 400:1 400:1 volume ratioProperties of jet fuel product Density 0.8080 0.8101 0.7981 0.8110 (20°C.), g/cm³ Distillation ASTM D 86 range, ° C. t IBP/10% 147/164 150/164146/159 150/163 30%/50% 177/198 179/200 169/189 178/200 70%/90% 218/243220/246 210/238 221/245 98%/FBP 260/263 262/265 260/264 261/264 Smokingpoint, 27 28 31 26 mm Aromatics, v % 5 4 0.7 7

[0043] TABLE 6 Results of diesel hydrosaturation of the presentinvention Example No. Example 4 Example 5 Feedstock ComparativeComparative Example 2 Example 2 Catalyst Catalyst B Catalyst A Processconditions Hydrogen partial pressure, 2.0 1.5 MPa Reaction temperature,° C. 220 200 LHVSV*, h⁻¹ 2.0 2.0 Hydrogen/oil volume ratio 400:1 400:1Properties of diesel product Density (20° C.), g/cm³ 0.8405 0.8386Distillation range (° C., ASTM 265-343 265-343 D 86) Aromatics, v % 14.112.2 Cetane number 53 54

What is claimed is:
 1. A medium-pressure hydrocracking process, comprising the steps of contacting feed oil with a hydrocracking catalyst in a hydrocracking system under a medium pressure and hydrocracking conditions; separating the hydrocraking reaction product into a vapor fraction which is recycled to the hydrocracking system as recycling hydrogen, and a liquid fraction which is further separated in a separation system to produce distillates including jet fuel and/or diesel (hereinafter referred to as hydrocracked jet fuel and/or diesel) cuts; feeding a part or all of the hydrocracked jet fuel and/or diesel cuts into a hydrosaturation system where the cuts come into contact with a hydrosaturation catalyst and react with fresh hydrogen under hydrosaturation conditions; separating the hydrosaturation reaction product into a hydrogen-containing vapor which enters into the hydrocracking system as make-up hydrogen, and jet fuel and/or diesel (hereinafter referred to as the hydrosaturated jet fuel and/or diesel) which enter into a separation system for processing.
 2. The process according to claim 1, wherein a part or all of the hydrocracked jet fuel cut enters into a hydrosaturation system for processing.
 3. The process according to claim 1, wherein a part or all of the hydrocracked diesel cut enters into a hydrosaturation system for processing.
 4. The process according to claim 1, wherein a part or all of the hydrocracked jet fuel and diesel cuts enter into a hydrosaturation system for processing.
 5. The process according to claim 1, wherein all of the hydrocracked jet fuel and/or diesel cuts enter into a hydrosaturation system for processing, and the hydrosaturated jet fuel and/or diesel enter into an individual separation system for processing, which then separately leaves the equipment as products.
 6. The process according to claim 1, wherein a part of the hydrocracked jet fuel and/or diesel cuts enter into a hydrosaturation system for processing, and the hydrosaturated jet fuel and/or diesel cuts enter into an individual separation system for processing, which then mixes with the other part of the corresponding hydrocracked jet fuel and/or diesel cuts and separately leaves the equipment as products.
 7. The process according to claim 1, wherein both the liquid fraction of the hydrocracking reaction product and the hydrosaturated jet fuel and/or diesel enter the same separation system for fractionation together, and a part of the separated jet fuel and/or diesel cuts enter into the hydrosaturation system for processing, and the remainder leaves the equipment as products.
 8. The process according to claim 1, wherein said hydrosaturation catalyst is a reduced catalyst with one or more metals of Groups VIB and/or VIII of the Periodic Table as the hydrogenation components.
 9. The process according to claim 1, wherein the hydrocracking reaction is carried out under a pressure of 4.0-10.0 MPa, at a temperature of 360-400° C., with a hydrogen/oil volume ratio of 800:1-1500:1 and a liquid hourly volume space velocity of 0.5-1.5 h⁻¹.
 10. The process according to claim 1, wherein the hydrosaturation reaction is carried out under a pressure of 0.5-3.0 MPa, at a temperature of 100-280° C., with a hydrogen/oil volume ratio of 200:1-1000:1, and a liquid hourly volume space velocity of 1.0-6.0 h³¹ ¹.
 11. The process according to claim 1, wherein said fresh hydrogen comes from a hydrogen-production system or the pipe net of the refinery and contains no such impurities as H₂S and NH₃, which is used directly in the process without being additionally pressurized.
 12. The process according to claim 8, wherein said one or more metals is/are selected from the group consisting of Pt, Ni, and Pd.
 13. The process according to claim 9, wherein said pressure is 4.0-8.0 MPa.
 14. The process according to claim 10, wherein said temperature is 100-250° C., and said pressure is 1.0-2.0 MPa.
 15. The process according to claim 7, wherein the weight ratio of said jet fuel and/or diesel distillate entering into the hydrosaturation system to those leaving the system as jet fuel and/or diesel products is 1:6-6:1. 